Ecophysiological Responses Of Typical Harmful Algal Bloom Species To Phosphorus

The study on ecophysiological responses of typical HAB species to nutrients (in particular phosphorus) were carried out using field survey, ship-based mesocosm experiments and lab-based incubation experiments in the high frequency HAB areas in the Yangtze River estuary and its adjacent East China Sea, southern Taiwan Strait and Xiamen Harbour. The phosphorus status of natural phytoplankton and the effects of nutrients on phytoplankton community structure were evaluated. The strategies of typical HAB species to the variations of environmental phosphorus were emphasized on, and whether the typical HAB species advantaged in competing for phosphorus and its mechanisms were discussed. The main results were as follows:1. Alkaline phosphatase activity (APA) showed that phytoplankton in the study areas suffered phosphorus (P) stresses with different degrees, with significance during bloom occurrence in sea areas in the Yangtze River estuary. All results from nutrients, APA and mesocosm enrichment experiments on board indicated that phytoplankton was P limited in the high frequency HAB areas in the Yangtze River estuary during spring. In the bloom period at the coastal upwelling zone in southern Taiwan Strait during summer, phytoplankton's P-stress status strengthened. During the spring (April ~ May) of 2002, 2003 and 2005, phytoplankton communities were under P stress in the Yangtze River estuary and its adjacent East China Sea (except the area just outside the Yangtze River estuary during the spring of 2005). P stress degrees strengthened during the bloom period in 2003. Size - fractionated APA indicated that phytoplankton was the main contributor of total APA. During the spring of 2005, high percentages of ELF labeling of the dominant dinoflagellates suggested that they suffered severe P stress and were the main contributors of AP while very low percentages of ELF labeling were found among Chrysophyta and diatom, indicating that they were not P stressed or slightly P stressed.During the summer (July ~ August) of 2004, phytoplankton community suffered P stress in southern Taiwan Strait, in particular during the bloom period in the coastal upwelling zone. High percentages of ELF labeling of dinoflagellates showed that they were under severe P-stress status. Besides, the dominant species diatom, such as...